| The composite system of the fresh-air supply system and radiant air cooling system is modified to provide a comfortable thermal environment and acceptable indoor quality in order to address the issues of insufficient fresh-air rate and poor indoor air quality of separate radiant air conditioning systems.There are already a variety of fresh-air supply techniques available,but research on how each affects the thermal environment of a radiant air conditioning room is scarce.Few studies have been done to date on the efficacy of air supply and air pollution discharge by various fresh-air supply systems in radiant air cooling rooms.The bedroom of the residential model room with the installation of underfloor air distribution+floor radiant heating system was experimentally tested.The parameters of the room’s pollutant concentration distribution and interior thermal environment were studied.According to the results of the experiment,the bedroom’s interior temperature during low-temperature radiant heating reaches its peak at around 190 minutes,and then gradually becomes stable.The stabilization temperature setting is slightly lower than the desired temperature.The difference in head and foot temperatures while sitting and standing amounts to 0.3℃ and 0.6℃,respectively.The interior temperature is always lower when it is close to the ceiling.Personnel are not bothered by the different temperature between head and foot.In this test,the indoor temperature is mainly influenced by the floor radiant temperature and outdoor temperature.The number of individuals in the room,the fresh air rate,and the fresh air temperature have less of an impact on the indoor temperature.The placement of interior testers and the location of the fresh air outlet have the main impacts on the vertical distribution of indoor CO2 concentration.The number of testers and the fresh air rate are the main factors affecting indoor CO2 concentration.The CO2 concentration increases by about 350 ppm for each additional person in the bedroom.A numerical model of the low-temperature radiant air-conditioned room under three fresh air modes,such as ceiling air supply,underfloor air distribution,and impinging jet supply,was established.The effects of the fresh-air supply mode,fresh air temperature,fresh air rate,and other factors on the thermal environment and air quality of the radiant air conditioning room were simulated and analyzed.According to the simulation results,the fresh-air supply mode under winter conditions has little impact on the indoor temperature field,airflow field,and PMV-PPD index distribution.When the impinging jet supply mode is used,the room has the greatest mean temperature,the most uniform temperature distribution,the highest indoor PMV value,and is the closest to thermal neutrality.The fresh air rate and fresh air temperature have a slight effect on the uniformity of temperature distribution and a certain effect on the average indoor temperature,and the impact on the average indoor temperature is about 0.3～0.6℃.The distribution of the PMV-PPD index,the indoor temperature field,the airflow field,and the humidity field are all little affected by the fresh-air supply mode during the summer.The impact on the average indoor temperature,head-foot temperature difference,relative humidity,and human skin wetness can be ignored.The fresh air rate and fresh air temperature have a certain impact on the average temperature of the radiant cooling room,and the impact range is about 0.3～0.7℃.Under winter and summer conditions,the average indoor air speed of the radiation+fresh air air-conditioning room is low,all below 0.05m/s,with no sense of blowing wind.The temperature distribution in the vertical direction of the room is higher when it is close to floor and lower when it is close to the ceiling,and the temperature difference between the head and foot is negative,meeting the requirements of ISO7730 standard.The simulation results show that the fresh-air supply mode has less influence on the average air age and average CO2 concentration in winter and summer conditions.Under the condition of a high air rate(120m3/h),the average air age of the breathing area of the room supplied with impinging jet is the minimum.Under the condition of a low air rate(60m3/h),the average air age of the breathing area of the room with air supply from the ceiling is the minimum.The difference in the average air age of the breathing area corresponding to different fresh air supply modes is no more than 5.7%.Among the three air supply modes,the average CO2 concentration in the breathing zone of the room under the underfloor air distribution is the lowest.The air supply mode,air supply temperature,and the fresh air rate have less influence on the uniformity of CO2 concentration distribution.The air exchange efficiency under the high air rate condition is between 0.64～0.67,and the air exchange efficiency under the small high air rate condition is between 0.77～0.86.The larger the high air rate,the smaller the air exchange efficiency.The air exchange efficiency in winter conditions is slightly higher than that in summer conditions,and the air exchange efficiency under underfloor air distribution is the lowest.The effect of the fresh air system parameters on the emission efficiency is very small.To analyze the influence of the uneven distribution of indoor CO2 concentration on fresh air demand,the CO2 concentration field of the ceiling air supply+ceiling radiant cooling room was simulated under different conditions of outdoor CO2 concentration and fresh air rate.The upper value of indoor CO2 concentration is obtained by eliminating the first 5%concentration of the observation point in the breathing zone,and then the per capita fresh air demand corresponding to the indoor CO2 concentration limit of 1000ppm is predicted.The results show that the fresh air rate is 8%～9%higher than the theoretical value of the current standard.Therefore,it is determined that the fresh air rate of the residential air conditioning system should be multiplied by 1.1 correction coefficient based on the calculation results of the current national norms. |
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